The present invention relates to a drive mechanism for moving an air guide arrangement provided in a motor vehicle from a retracted rest position into an extended operating position and vice versa, whereby the drive mechanism includes a toothed segment rotatably supported about a shaft which is operatively connected with an adjusting lever of the air guide arrangement.
A drive mechanism of the aforementioned type is described in the (not-yet-published) German Pat. application No. P 36 15 84.5. In this drive mechanism, the toothed segment is constructed in one piece with the adjusting lever, as a result of which a rigid through-drive from the transmission pinion by way of the toothed segment to the adjusting lever of the air guide arrangement takes place both during the retracting operation as also during the extending operation of the air guide arrangement. This arrangement entails the disadvantage that the over-travel of the electric motor of the drive mechanism strongly varies with the temperature (summer/winter) and additionally is different from vehicle to vehicle. As a result thereof, the drive system is more or less stressed when the air guide arrangement runs up against the abutments on the side of the body which under certain circumstances can lead to breakage of the flexible shafts of the drive mechanism.
In order to be able to compensate occurring tolerances between the air guide arrangement and the adjoining body, the abutments must be constructed adjustable in this arrangement which considerably increases the installation expenditure. Furthermore, the motor is stopped abruptly if the electrical limit switches for the motor are out of adjustment owing to installation errors.
It is the object of the present invention to undertake in a drive mechanism for an adjustable air guide arrangement such measures that error sources conditioned on installation or manufacture such as over-travel of the electric motor or limit switches which are out of adjustment can be compensated.
The underlying problems are solved according to the present invention in that the toothed segment and the adjusting lever are supported on the shaft independently of one another and are held in a predetermined position relative to one another by a spring element disposed therebetween, and in that an entrainment member of the toothed segment so cooperates with a slot opening of the adjusting lever that during the extension of the air guide arrangement into the operating position, a rigid force transmission takes place between the toothed segment and the adjusting lever whereas in the end phase of the closing operation of the air guide arrangement, the entrainment member is decoupled from an upper boundary edge of the slot opening and is displaced toward a lower boundary edge of the slot opening by overcoming the spring tension of the spring element.
The advantages principally achieved with the present invention reside in that during the end phase of the closing operation of the air guide arrangement, the occurring error sources conditioned on installation and manufacture (motor over-travel, incorrect adjustment of limit switches, etc.) can be compensated at the place of the decoupling by the decoupled arrangement of the toothed segment and the adjusting lever as well as by the spring element.
During the closing movement of the air guide arrangement, the toothed segment is decoupled by way of the slot opening from an upper boundary edge in the direction toward a lower boundary edge as soon as the air guide arrangement contacts the abutments on the body side but the motor has not yet been de-energized (out of adjustment limit switches) or over-travels. No abrupt stopping of the motor thus takes place any longer and the stress forces of the flexible shafts are considerably smaller owing to the larger travel which the system now can undertake. The stressing is absorbed by the spring element. During the extension of the air guide arrangement, the drive system has the full torque of the motor available in order to move, for example, a frozen-in air guide arrangement into its extended operating position. This is achieved in that the entrainment member of the toothed segment abuts directly at the upper boundary of the slot opening. The defined elasticity in the force transmission can be varied during the closing operation by the angle .beta. of the slot opening in the adjusting lever, respectively, by the spring design. A rattling of the air guide arrangement in the rest position is prevented in that the air guide arrangement abuts under prestress at the abutments on the body side.